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Understanding photocatalytic overall water splitting on CoO nanoparticles: Effects of facets, surface stoichiometry, and the CoO/water interface
Journal of Catalysis ( IF 7.3 ) Pub Date : 2018-07-06 , DOI: 10.1016/j.jcat.2018.06.021
Kyoung-Won Park , Alexie M. Kolpak

Unlike CoO micropowder, which is unable to split water, CoO nanoparticles have been observed to photocatalytically split water into H2 and O2 at room temperature without an externally applied potential or co-catalyst. The photocatalytic activity of CoO nanoparticles has been suggested to stem from an upwards shift in the band edges relative to bulk CoO such that the conduction and valence band edges span the water redox potentials. However, the origin of this shift in the band edges is unknown. In this study, we use first-principles density functional theory (DFT) calculations to explore the thermodynamically stable surface configurations of CoO as a function of oxygen chemical potential. We show that the band edge positions are sensitive to surface chemistry which is determined by surface orientation, adsorbates, and stoichiometry, and thus growth conditions and operating environment. In particular, we predict that CoO nanoparticles have fully hydroxylated CoO(1 1 1) facets, with band edges spanning the water redox potentials, while larger CoO particles (such as CoO micropowders) have a full monolayer of hydrogen on the CoO(1 1 1) facets, with a band alignment that favors water oxidation but not water reduction. Furthermore, we demonstrate that explicit inclusion of liquid water is crucial for accurately predicting the band edge positions, and thus photocatalytic behavior, of CoO in an aqueous solution. Our work explains why photocatalytic overall water splitting has only been observed on CoO nanoparticles, and provides new insights into the relationships between environmental conditions, surface structure, and band alignment, which may lead to new approaches for optimizing activity in CoO and other oxide photocatalysts.



中文翻译:

了解CoO纳米颗粒上的光催化整体水分解:刻面,表面化学计量以及CoO /水界面的影响

与无法分解水的CoO微粉不同,已观察到CoO纳米颗粒可将水光催化分解为H 2和O 2在室温下没有外部施加的电势或助催化剂。已经提出,CoO纳米颗粒的光催化活性源于带边缘相对于本体CoO的向上移动,使得导带和价带边缘跨越水的氧化还原电势。然而,在频带边缘的这种偏移的起源是未知的。在这项研究中,我们使用第一原理密度泛函理论(DFT)计算来探索CoO的热力学稳定表面构型与氧化学势的关系。我们表明,带的边缘位置对表面化学敏感,这是由表面取向,吸附物和化学计量关系决定的,因而决定了生长条件和操作环境。特别是,我们预测CoO纳米颗粒具有完全羟基化的CoO(1 1 1)面,带的边缘跨越了水的氧化还原电位,而较大的CoO颗粒(例如CoO微粉)在CoO(1 1 1)面上具有完整的氢单层,其带取向有利于水的氧化而不是水的还原。此外,我们证明了明确包含液态水对于准确预测水溶液中CoO的能带边缘位置以及光催化行为至关重要。我们的工作解释了为什么仅在CoO纳米颗粒上观察到光催化整体水分解的原因,并提供了对环境条件,表面结构和能带排列之间关系的新见解,这可能会导致优化CoO和其他氧化物光催化剂活性的新方法。而较大的CoO颗粒(例如CoO微粉)在CoO(1 1 1)面上具有完整的氢单层,其带取向有利于水的氧化而不是水的还原。此外,我们证明了明确包含液态水对于准确预测水溶液中CoO的能带边缘位置以及光催化行为至关重要。我们的工作解释了为什么仅在CoO纳米颗粒上观察到光催化整体水分解的原因,并提供了对环境条件,表面结构和能带排列之间关系的新见解,这可能会导致优化CoO和其他氧化物光催化剂活性的新方法。而较大的CoO颗粒(例如CoO微粉)在CoO(1 1 1)面上具有完整的氢单层,其带取向有利于水的氧化而不是水的还原。此外,我们证明了明确包含液态水对于准确预测水溶液中CoO的能带边缘位置以及光催化行为至关重要。我们的工作解释了为什么仅在CoO纳米颗粒上观察到光催化整体水分解的原因,并提供了对环境条件,表面结构和能带排列之间关系的新见解,这可能会导致优化CoO和其他氧化物光催化剂活性的新方法。我们证明,明确包含液态水对于准确预测水溶液中CoO的能带边缘位置以及因此的光催化行为至关重要。我们的工作解释了为什么仅在CoO纳米颗粒上观察到光催化整体水分解的原因,并提供了对环境条件,表面结构和能带排列之间关系的新见解,这可能会导致优化CoO和其他氧化物光催化剂活性的新方法。我们证明,明确包含液态水对于准确预测水溶液中CoO的能带边缘位置以及因此的光催化行为至关重要。我们的工作解释了为什么仅在CoO纳米颗粒上观察到光催化整体水分解的原因,并提供了对环境条件,表面结构和能带排列之间关系的新见解,这可能会导致优化CoO和其他氧化物光催化剂活性的新方法。

更新日期:2018-07-06
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